At present, radiograph CT systems such as X-ray CT system are widely used in various medical institutions for three-dimensional imaging of the regions of interest of the subjects to assist the clinicians to achieve an accurate medical diagnosis of the subjects.
In a radiograph CT system, a radiation source generating cone-shaped radiation beams and a radiation detector arranged on the other side of a subject relative to the radiation source and detecting the radiation beams rotate around a rotation center between the radiation source and the radiation detector. Projection data generated by the radiation beams transmitting through the subject are collected; based on the collected projection data, an image of the region of interest of the subject is reconstructed; and then the reconstructed CT image is displayed on an image display device.
In a radiograph CT system, a collimator is generally provided between the radiation source and the subject to be detected. By adjusting a width of the aperture of the collimator, the width of the radiation beams in a direction parallel to the subject is controlled so as to control a thickness of the scan slice.
A conventional collimator generally has at least two different motor drive systems to meet the requirements of multi-slot opening and Z tracking. Such a collimator comprises at least two gates or cams, which are driven by at least two different motor drive systems, and hence have higher cost, despite the fact that excellent performance is ensured by using at least two motor drive systems.
Some newly developed collimators use a single-motor drive system to meet the requirements of opening and Z tracking. Typically, such type of collimator comprises a plate or a star-shaped rotor having a plurality of slots driven by a single-motor drive system. Each slot corresponds to a collimator aperture of a different width. Said type of collimator can only show apertures of a fixed number and width; and during its rotation, the star-shaped rotor for Z tracking will include a different amplitude coefficient, due to a difference in distance from the two beam guiding edges to the curved surface detector.